Hydrocarbons such as oil and gas are usually recovered from a subterranean formation using wellbores drilled into the formation. During the life of a well, it may be necessary to set a plug for sidetracking, lost-circulation control, zone isolation and/or well abandonment purposes.
Zonal isolation may be necessary in many wells and is achieved when securing a casing string inside a section of the wellbore typically by pumping cement into the annular space defined by the inner surface of the wellbore wall and the outer surface of the casing string.
Well abandonment is usually considered when a well reaches its economic limit and becomes a financial liability. In this process, production tubing is removed from the cased wellbore and sections of the wellbore are generally sealed off with a cement plug (which may be many metres in height) to plug the wellbore at that location and therefore isolate the potential flow path between the various gas or oil and water zones from each other, as well as the surface.
Both procedures require some kind of barrier or support device placed inside the wellbore either temporarily or permanently, but with sufficient strength to withstand the pushing/pumping force provided by the weight of the cement placed on top of the support device.
Similarly, when cementing a casing in place in, for example, a gas cavern, salt cavern, coal bed, methane well etc., it is desirable to provide a reliable and cost effective support structure that can be easily installed and removed.
In a particular example for abandoning or suspending a well, the so called plug cementing is an essential operation performed in accordance with regulatory guidelines under a variety of well conditions. Safety regulations require between 150 m and 300 m of a column of cement to be provided in the area to be abandoned or suspended. The column of cement is typically delivered into the wellbore via a drillstring (i.e. a string of drill pipe such as OCTG tubulars). In order to prevent slumping of the heavier cement into the well fluid below the plug, a physical barrier is used to hold the cement in place while the cement hardens to form a plug.
FIG. 1 discloses an example of a known cement support tool (Perigon CST™ tool) 1 that is delivered to a location within the wellbore 3 via a drill pipe string 2. During delivery, the cement support tool 1 is folded together like an umbrella stored inside a transport tube 4 before it is pushed into the drill pipe string 2 using a push rod 5. The cement support tool 1 is then pushed through the drill pipe string 2 by the following cement 6 until it leaves the lower most end of the drill pipe string 2 at which point it unfolds and contacts the wellbore walls 7. In the unfolded state, a membrane 8 of the cement support tool 1 fills the inner diameter of the wellbore 3 helping to prevent wellbore fluid below the cement support tool 1 from mixing with the cement 6 that is pumped down the drill pipe string 2 into the wellbore 3.
However, the cement support tool 1 described above does not provide a particularly strong barrier due to the limited gripping force that can be provided by the unfolded wire arrangement, so that not much cement weight can be put on top of the cement support tool 1 before it moves. Additionally, cement is delivered into the wellbore after the installation of the support tool 1 resulting in major time losses.
FIG. 2 illustrates an improvement over the above described device and as disclosed in WO2012/160380. An improved device 100 of WO2012/160380 comprises an inflatable elastomeric element 102 adapted to expand into a substantially cylindrical shape when inflated with a fluid to block the wellbore 120 and to retain itself in the position blocking the wellbore 120. The inflatable element 102 is delivered to a distal end of a string 106 by being pumped along an inner bore of the string 106 by the same fluid (cement slurry 124) which will be used for plugging the wellbore 120. Once positioned at the distal end of the string 106, the inflatable element 102 is inflated with the slurry 124. The inflatable element 102 has a pressure sensitive resiliently deformable disconnect member 108 for detaching the inflatable element 102 from the string 106 once the inflatable element 102 has expanded sufficiently to block the wellbore 120 and to retain itself in the position blocking the wellbore 120. The disconnect member 108 is retained within an inner bore of the string 106 while the inflatable element 102 is being inflated. The disconnect member 108 deforms when the pressure acting on the disconnect member 108 exceeds a predetermined pressure, which is not less than the pressure needed to expand the inflatable element 102 to block the wellbore 120 (as shown in phantom lines in FIG. 2), and passes through an outlet 126 at the distal end of the string 106 thereby disconnecting the inflatable element 102 from the string 106. The inflatable element 102 has annular ribs 112 provided around its outer circumference for gripping and sealing against a wellbore wall 122. After the inflatable element has detached from the string 106 into the position blocking the wellbore 120, the cement slurry 124 is continued to be pumped through and out of the string 106 into the wellbore above the inflatable element 102. At the same time the string 106 begins to be gradually pulled out of the wellbore 120 at an appropriate speed so that a required length of the wellbore 120 becomes filled with the slurry. The slurry is then allowed to harden and thus a secure plug inside the wellbore 120 formed. In this arrangement, delivery and installation of the support device 100 and pumping cement slurry 124 down the well bore are carried out simultaneously.
Although providing an improvement over the pre-existing devices, the device of WO2012/160380 has a relatively low reliability because of the relatively high rate of failure of the device during deployment.
Accordingly, it is an object of the present invention to obviate and/or mitigate the above disadvantages of the prior art and to provide an improved support device for use in a wellbore, the device having improved support strength and sealing properties, higher reliability and cost efficiency than prior art support devices. A further object of the present invention is to provide an improved method for deploying a support device in a wellbore.